metaprogramming and politics

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Archive for October 2013

Defeating Sauron with the “Trust on first use” principle

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photo from Alexandre Duret-Lutz Gandalf and Frodo did the right thing when they went for destroying the power of the all-seeing eye. The idea of a central power that knows everything undermines our ability to self-govern and influence important changes in society, it undermines a foundation of democracy.

As against Sauron, it seems like an impossible fight to try to protect our communication against present-day espionage cartels.  I see glimmers of hope, though. Certainly not much in the political space. Somehow our politicians are themselves too interested to use the eye on select targets — even if only the ones which Sauron allows them to see.

My bigger hope lies with technologists who are working on designing better communication systems. We still have time during which we can reduce Sauron’s sight. But to begin with, how do we prevent passive spying attacks against our communications?

A good part of the answer lies in the Trust on first use principle. The mobile Threema application is a good example: when two people first connect with each other, they exchange communication keys and afterwards use it to perform end-to-end encrypted communications. The key exchange can happen in full sight of the eye, yet the subsequent communication will be illegible. No question, the eye can notice that the two are communicating with unknown content but if too many of them do that this fact becomes less significant.

Of course, the all-seeying eye can send a Nazgul to stand in the middle of the communication to deceive both ends and listen in. But it needs to do so from the beginning and continously if it wants to avoid the victims from noticing. And those two can at any time meet to verify their encryption keys and would realize there  was a Nazgul-in-the-middle attack.

By contrast, both SSL and GPG operate with a trust model where we can hear Sauron’s distant laughter. The one is tied to a thousand or so “root authorities”, which can be easily reined in as need be. The other mandates and propagates such a high level of initial mistrust between us that we find it simply too inconvenient to use.

Societies and our social interactions are fundamentally build on trust. Let’s design systems which build on initial trust and which help to identify after-the-fact when it was compromised. If the eye has bad dreams, then i am sure massively deployed trust-on-first-use communication systems are among them.

Written by holger krekel

October 26, 2013 at 7:04 am

pytest-2.4.0: new fixture features, many bug fixes

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The just released pytest-2.4.0 brings many improvements and numerous bug fixes while remaining plugin- and test-suite compatible (apart from a few supposedly very minor incompatibilities). See below for a full list of details. New feature highlights:
  • new yield-style fixtures pytest.yield_fixture, allowing to use existing with-style context managers in fixture functions.
  • improved pdb support: import pdb ; pdb.set_trace() now works without requiring prior disabling of stdout/stderr capturing. Also the --pdb options works now on collection and internal errors and we introduced a new experimental hook for IDEs/plugins to intercept debugging: pytest_exception_interact(node, call, report).
  • shorter monkeypatch variant to allow specifying an import path as a target, for example: monkeypatch.setattr("requests.get", myfunc)
  • better unittest/nose compatibility: all teardown methods are now only called if the corresponding setup method succeeded.
  • integrate tab-completion on command line options if you have argcomplete configured.
  • allow boolean expression directly with skipif/xfail if a “reason” is also specified.
  • a new hook pytest_load_initial_conftests allows plugins like pytest-django to influence the environment before conftest files import django.
  • reporting: color the last line red or green depending if failures/errors occured or everything passed.

The documentation has been updated to accomodate the changes, see http://pytest.org

To install or upgrade pytest:

pip install -U pytest # or
easy_install -U pytest

Many thanks to all who helped, including Floris Bruynooghe, Brianna Laugher, Andreas Pelme, Anthon van der Neut, Anatoly Bubenkoff, Vladimir Keleshev, Mathieu Agopian, Ronny Pfannschmidt, Christian Theunert and many others.

may nice fixtures and passing tests be with you,

holger krekel

Changes between 2.3.5 and 2.4

known incompatibilities:

  • if calling –genscript from python2.7 or above, you only get a standalone script which works on python2.7 or above. Use Python2.6 to also get a python2.5 compatible version.
  • all xunit-style teardown methods (nose-style, pytest-style, unittest-style) will not be called if the corresponding setup method failed, see issue322 below.
  • the pytest_plugin_unregister hook wasn’t ever properly called and there is no known implementation of the hook – so it got removed.
  • pytest.fixture-decorated functions cannot be generators (i.e. use yield) anymore. This change might be reversed in 2.4.1 if it causes unforeseen real-life issues. However, you can always write and return an inner function/generator and change the fixture consumer to iterate over the returned generator. This change was done in lieu of the new pytest.yield_fixture decorator, see below.

new features:

  • experimentally introduce a new pytest.yield_fixture decorator which accepts exactly the same parameters as pytest.fixture but mandates a yield statement instead of a return statement from fixture functions. This allows direct integration with “with-style” context managers in fixture functions and generally avoids registering of finalization callbacks in favour of treating the “after-yield” as teardown code. Thanks Andreas Pelme, Vladimir Keleshev, Floris Bruynooghe, Ronny Pfannschmidt and many others for discussions.

  • allow boolean expression directly with skipif/xfail if a “reason” is also specified. Rework skipping documentation to recommend “condition as booleans” because it prevents surprises when importing markers between modules. Specifying conditions as strings will remain fully supported.

  • reporting: color the last line red or green depending if failures/errors occured or everything passed. thanks Christian Theunert.

  • make “import pdb ; pdb.set_trace()” work natively wrt capturing (no “-s” needed anymore), making pytest.set_trace() a mere shortcut.

  • fix issue181: –pdb now also works on collect errors (and on internal errors) . This was implemented by a slight internal refactoring and the introduction of a new hook pytest_exception_interact hook (see next item).

  • fix issue341: introduce new experimental hook for IDEs/terminals to intercept debugging: pytest_exception_interact(node, call, report).

  • new monkeypatch.setattr() variant to provide a shorter invocation for patching out classes/functions from modules:

    monkeypatch.setattr(“requests.get”, myfunc)

    will replace the “get” function of the “requests” module with myfunc.

  • fix issue322: tearDownClass is not run if setUpClass failed. Thanks Mathieu Agopian for the initial fix. Also make all of pytest/nose finalizer mimick the same generic behaviour: if a setupX exists and fails, don’t run teardownX. This internally introduces a new method “node.addfinalizer()” helper which can only be called during the setup phase of a node.

  • simplify pytest.mark.parametrize() signature: allow to pass a CSV-separated string to specify argnames. For example: pytest.mark.parametrize("input,expected",  [(1,2), (2,3)]) works as well as the previous: pytest.mark.parametrize(("input", "expected"), ...).

  • add support for setUpModule/tearDownModule detection, thanks Brian Okken.

  • integrate tab-completion on options through use of “argcomplete”. Thanks Anthon van der Neut for the PR.

  • change option names to be hyphen-separated long options but keep the old spelling backward compatible. py.test -h will only show the hyphenated version, for example “–collect-only” but “–collectonly” will remain valid as well (for backward-compat reasons). Many thanks to Anthon van der Neut for the implementation and to Hynek Schlawack for pushing us.

  • fix issue 308 – allow to mark/xfail/skip individual parameter sets when parametrizing. Thanks Brianna Laugher.

  • call new experimental pytest_load_initial_conftests hook to allow 3rd party plugins to do something before a conftest is loaded.

Bug fixes:

  • fix issue358 – capturing options are now parsed more properly by using a new parser.parse_known_args method.
  • pytest now uses argparse instead of optparse (thanks Anthon) which means that “argparse” is added as a dependency if installing into python2.6 environments or below.
  • fix issue333: fix a case of bad unittest/pytest hook interaction.
  • PR27: correctly handle nose.SkipTest during collection. Thanks Antonio Cuni, Ronny Pfannschmidt.
  • fix issue355: junitxml puts name=”pytest” attribute to testsuite tag.
  • fix issue336: autouse fixture in plugins should work again.
  • fix issue279: improve object comparisons on assertion failure for standard datatypes and recognise collections.abc. Thanks to Brianna Laugher and Mathieu Agopian.
  • fix issue317: assertion rewriter support for the is_package method
  • fix issue335: document py.code.ExceptionInfo() object returned from pytest.raises(), thanks Mathieu Agopian.
  • remove implicit distribute_setup support from setup.py.
  • fix issue305: ignore any problems when writing pyc files.
  • SO-17664702: call fixture finalizers even if the fixture function partially failed (finalizers would not always be called before)
  • fix issue320 – fix class scope for fixtures when mixed with module-level functions. Thanks Anatloy Bubenkoff.
  • you can specify “-q” or “-qq” to get different levels of “quieter” reporting (thanks Katarzyna Jachim)
  • fix issue300 – Fix order of conftest loading when starting py.test in a subdirectory.
  • fix issue323 – sorting of many module-scoped arg parametrizations
  • make sessionfinish hooks execute with the same cwd-context as at session start (helps fix plugin behaviour which write output files with relative path such as pytest-cov)
  • fix issue316 – properly reference collection hooks in docs
  • fix issue 306 – cleanup of -k/-m options to only match markers/test names/keywords respectively. Thanks Wouter van Ackooy.
  • improved doctest counting for doctests in python modules — files without any doctest items will not show up anymore and doctest examples are counted as separate test items. thanks Danilo Bellini.
  • fix issue245 by depending on the released py-1.4.14 which fixes py.io.dupfile to work with files with no mode. Thanks Jason R. Coombs.
  • fix junitxml generation when test output contains control characters, addressing issue267, thanks Jaap Broekhuizen
  • fix issue338: honor –tb style for setup/teardown errors as well. Thanks Maho.
  • fix issue307 – use yaml.safe_load in example, thanks Mark Eichin.
  • better parametrize error messages, thanks Brianna Laugher
  • pytest_terminal_summary(terminalreporter) hooks can now use “.section(title)” and “.line(msg)” methods to print extra information at the end of a test run.

Written by holger krekel

October 1, 2013 at 9:40 am

Posted in metaprogramming

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